Damascus has strongly denounced as a “war crime” a deadly strike carried out by the US-led military coalition against pro-government forces in Syria's eastern Dayr al-Zawr province, saying US presence in the country is "illegitimate."

The Syrian Ministry of Foreign Affairs and Expatriates condemned the strike in two separate letters sent to UN Secretary General Antonio Guterres and the rotating president of the UN Security Council on Thursday, saying the air raid was “a crime against humanity.”

It further lambasted Washington for using “the excuse of fighting terrorism to set up illegitimate bases on Syrian territory.”

The US military said late Wednesday that it had killed at least 100 pro-government fighters in Syria to allegedly fend off an attack on the so-called US-backed Syrian Democratic Forces (SDF) in Dayr al-Zawr province.

“We demand that the international community … condemn this massacre and hold the [US-led] coalition responsible for it,” added the ministry in the letters, as cited by Syria’s official news agency, SANA.

It also demanded, once again, that the “this illegitimate coalition” be dissolved.

“This aggression reveals once again, without any doubt, the real function of this alliance and the role played by Washington in supporting the Daesh Takfiri terrorist group, as it did in the past,” the ministry further said.

Meanwhile, the Russian Defense Ministry said in a statement that the raid once “again showed that the US is maintaining its illegal presence in Syria not to fight the Daesh group, but to seize and hold Syrian economic assets.”

Back in December, Russian Foreign Minister Sergei Lavrov said that all foreign forces, including those of the US-led coalition that are present in Syria without any authorization from the Damascus government, had to withdraw from the Arab country after the total defeat of Daesh.

The US-led coalition has been conducting airstrikes against what are said to be Daesh targets inside Syria since September 2014 without any authorization from the Damascus government or a UN mandate. The military alliance has repeatedly been accused of targeting and killing civilians. It has also been largely incapable of fulfilling its declared aim of destroying Daesh.

Damascus has on several occasions called for US troops to leave Syria now that the fight against Daesh is over.

The Syrian government, backed by Russian air cover, has managed to push back the terrorists turf after turf. The Arab country flushed Daesh out of its last stronghold in November.